UFC light heavyweight champ Jon Jones has never lost his title in the octagon, but Thiago Santos came as close as anyone has previously after a split-decision result at UFC 239.

Jones, who has been stripped of belts in the past for anti-doping offences, emerged victorious in his second title defence, but it was far from convincing.

Jones attempted just 90 significant strikes in the 25-minute fight, the fewest in his last seven fights, and Santos fought the majority of the contest with a badly-injured leg.

When the 25-minute contest concluded, there was uncertainty about who was the winner. The first scorecard read was in favour of Santos, but then the next two went the way of the champion.

The Brazilian admitted the injury handicapped his ability to attack Jones.

"The first round wasn't anything Jon Jones did to me," he said afterwards. "I felt the knee go out and it really bothered my fight.

"Everyone saw I did everything I could fighting on a bum knee and I fought the whole fight like that."

In the co-main event, Amanda Nunes cemented her legacy with a first-round KO of former champion Holly Holm with a vicious head kick and follow-up punches.